This invention relates to a high-refractive-index optical silicone oil and to a high-refractive-index optical silicone oil mixture. More particularly, this invention relates to a high-refractive-index optical silicone oil and a high-refractive-index optical silicone oil mixture comprising a pentasiloxane having terminal aralkyl groups, wherein the oil has a refractive index from 1.45 to 1.50 at 25xc2x0 C.
Optical silicone oils, like optical adhesives and optical greases, are used as fillers between lenses and between prisms in optical devices and as fillers in the connectors used for optical fibers. However, when an optical silicone oil is employed as the fill between lenses or prisms or between the terminal surfaces of optical fibers, any residual bubbles present in the silicone oil and/or bubbles produced along the interface between the silicone oil and lens, prism, or optical fiber terminal function to scatter the transmitted light or optical signal and thereby cause flare or transmission losses. To counter this, low-viscosity phenyl-type silicone oils with viscosities (25xc2x0 C.) in the range from 1 to 70 mm2/s and refractive indices (25xc2x0 C.) in the range from 1.46 to 1.51 have been used as optical silicone oils. Unfortunately, the phenyl-type silicone oils typically have broad molecular weight distributions, which has led to the problem of timewise changes in the refractive index due to volatilization of the phenyl-type silicone oil in the low molecular weight region.
Within the realm of the 2-methylphenethyl-functional optical silicone oils, Japanese Laid Open (Kokai or Unexamined) Patent Application Number Hei 6-92973 (92,973/1994) teaches a disiloxane having a 2-methylphenethyl group at one or both terminals. Due to its narrow molecular weight distribution, this disiloxane offers the advantage of undergoing no change in refractive index even when some amount of volatilization occurs. However, the disiloxane itself still suffers from a high volatility.
The present inventors have discovered that the aforementioned problems can be solved by using a pentasiloxane having terminal aralkyl groups.
In specific terms, the object of the present invention is to provide a low-volatility high-refractive-index optical silicone oil and a low-volatility high-refractive-index optical silicone oil mixture that undergo very little change in refractive index upon volatilization.
The present invention is directed to a high-refractive-index optical silicone oil comprising a pentasiloxane having the formula:
RMe2SiO(Me2SiO)3SiMe2R
wherein Me is methyl, each R is independently a C8 to C12 aralkyl, and the silicone oil has a refractive index of from 1.45 to 1.50 at 25xc2x0 C.
The present invention is also directed to a method of preparing a high-refractive-index optical silicone oil having a refractive index of from 1.45 to 1.50 at 25xc2x0 C., comprising reacting a C8 to C12 aryl-containing olefin with a pentasiloxane having the formula:
xe2x80x83HMe2SiO(Me2SiO)3 SiMe2H
in the presence of a supported platinum catalyst.
The present invention is further directed to a high-refractive-index optical silicone oil mixture, comprising a pentasiloxane having the formula:
RMe2SiO(Me2SiO)3SiMe2R
wherein Me is methyl, each R is independently a C8 to C12 aralkyl, and a disiloxane having the formula:
RMe2SiOSiMe2R
wherein Me and R as defined above and wherein the mixture has a refractive index of from1.45 to 1.50 at 25xc2x0 C.
The present invention is still further directed to a method of preparing a high-refractive-index optical silicone oil mixture having a refractive index of from 1.45 to 1.50 at 25xc2x0 C., comprising reacting a C8 to C12 aryl-containing olefin with a mixture comprising a pentasiloxane having the formula:
HMe2SiO(Me2SiO)3SiMe2H
and a disiloxane having the formula:
HMe2SiOSiMe2H